A variable valve timing device (VVT) for adjusting opening and closing timing of an intake valve or an exhaust valve in an engine is known. The VVT is applied to the engine which includes a camshaft for operating the intake valve or the exhaust valve, and an engine output shaft, e.g., a crankshaft, which synchronously rotates the camshaft via a drive train such as a belt drive train and a gear train. The VVT may be installed in the drive train for transmitting driving force from the output shaft to the camshaft. The VVT includes a first rotor which rotates with either one of the camshaft and the output shaft, and a second rotor which rotates with the other one of the camshaft and the output shaft. The VVT may be configured as a displacement type rotary machine which varies relative rotational position of the first and second rotors by controlling operating fluid supplied to chambers. One type of the VVT is known as a vane type machine which includes a housing provided as one of the first and second rotors and a vane rotor provided as the other one. The housing and the vane rotor define at least one pair of an advancing chamber and a retarding chamber. Usually, the vane rotor divides a chamber defined in the housing into the advancing chamber and retarding chamber. The VVT further includes a fluid control devices and a control unit for controlling the fluid control devices to adjust a relative rotational position between the housing and the vane rotor. For example, the control unit controls fluid supply to the chambers and fluid discharge from the chambers.
In such a system, in order to supply sufficiently pressurized operating fluid, such as oil, it is necessary to begin operation of a pump well before starting control of the VVT. For example, in a case that a pump is driven by the output shaft of the engine, it is impossible to supply sufficiently pressurized fluid at an early stage of starting of the engine. Therefore, due to fluctuation torque on the camshaft caused by valve springs and insufficient pressure, the housing and the vane rotor may be adversely rotated and can not maintain a required relative rotational position.
To address the above-mentioned problem, the conventional VVT has a restriction mechanism such as a narrowly restricting lock mechanism which includes a lock pin and a lock slot to be engaged with each other. The lock pin is constructed to be projected to the projected position when a predetermined projecting condition is satisfied. If the lock pin in the projected position meets the lock slot, the lock pin is engaged with the lock slot to lock the housing and the vane rotor to be impossible to rotate relatively. The lock mechanism is operated to lock the housing and the vane rotor before an engine starting event. For example, the lock mechanism locks the rotors at a last stopping event of the engine. As a result, it is possible to keep the relative rotational position of the housing and the vane rotor at a predetermined position suitable for restarting the engine.
During a locking operation of the lock mechanism, the lock pin moves toward the lock slot in a rotating or orbiting manner as the housing and the vane rotor are relatively rotated. In detail, due to the fluctuation torque, the lock pin and lock slot approaches each other while slightly oscillating in an advancing direction and a retarding direction. Therefore, in some cases depending upon oscillating movement, the lock pin and the lock slot may not be able to be engaged before the engine and the pump completely are stopped.
To address the above-mentioned problem, the VVT disclosed in JP2002-357105 includes a guiding mechanism for guiding the lock pin in the projected position to the lock slot by a guide slot. The guide slot is formed to be overlapped with the lock slot. In other words, the lock slot is provided within a rotatable range defined by the lock pin and the guide slot. According to the VVT, the lock pin can be caught by the guide slot, then, is rotated toward the lock slot while rotatable range of the lock pin is restricted by the guide slot. Therefore, since the lock pin is rotated toward the lock slot under restricted state, it is possible to facilitate an engagement of the lock pin and the lock slot.